The overall objective of this proposed research is to establish the avian sarcoma virus (ASV) induced primary brain tumor in rats as an immunologic parallel of humans harboring morphologically and biologically similar brain tumors, using related quantitative and qualitative in vitro and in vivo immunologic probes. The proposed research is designed to assess immune function during the pre-tumor and tumor states. Lymphocytes from ASV inoculated rats will be quantitated via their cell surface receptors and their responsiveness to mitogens determined. Defects in macrophage function will be assessed employing a chemotaxis assay. The in vivo immune competence of ASV inoculated rats will be evaluated by measuring humoral antibody production and cutaneous skin reactivity at various times after immunization with particulate and soluble antigens. Antibody and cell-mediated tumor immunity as measured by 51Cr release assays, mixed lymphocyte-tumor reaction and lymphocyte blastogenesis to neural (normal and neoplastic) antigens will be determined. The mechanisms for the diminished general immunocompetence observed in tumor-bearing rats will be sought by characterizing cellular and/or humoral suppressor factors. Spleen cells from these rats will be fractionated on glass bead columns and the responsiveness of these fractions to mitogens and to tumor and/or neural antigens determined. The identity of the suppressor cell(s) will be determined by employing reconstitution experiments together with abrogation of suppressor cell activity by specific antisera and, finally, further fractionation of the cells based on functional and cell surface receptor characteristics. Classical chemical and biophysical techniques will be utilized to study and isolate the tumor induced serum suppressor factor(s) using as a monitor of suppressor activity the responsiveness of lymphocytes to mitogens and neural antigens. Experiments will also be conducted to identify substances (serum factors, antigen-antibody complexes, tumor cells, etc.) from tumor-bearing rats which induce suppressor cells.